Ballooned the valley pan gasket

[Dan Jones]

I somehow ballooned the intake manifold on the TR8's Rover V8.
On the little Rover/Buick, there is a gap between the bottom
of the intake manifold and the gasket.  The gasket is held on
by steel rails on the ends and the manifold on the sides but
the center is unsupported.  With the change from the Offy to
the Edelbrock intake manifold, my old air cleaner would not
clear so I swapped to a Moroso drop base unit.  The previous
owner spliced a PCV valve inline with the hose from the fitting
on the right hand valve cover which I routed to the air cleaner.
There is also a small fitting on left hand side that was routed
to the previous air cleaner but the Moroso didn't have a fitting
for it.  Initially, I just left it open.  I intended to drill
the switch to a different air cleaner and put a fitting on it.
For some reason, I decided to cap off the valve cover with a
small vacuum cap.  I ran it up to 100 MPH or so on the way to
work and when I got there I popped the hood to find oil pooled
on the intake gasket and the gasket bowed up in the middle.
Apparently, the crankcase pressurized enough to bow it and
pull it from the end seal rails enough to cause a leak.
I removed the vacuum cap, pushed the manifold back down
and cleaned off the oil and drove it home.  Unfortunately,
it is still leaking oil onto the manifold gasket, though not
as much as before.  Looks like, at a minimum, I'm going to
have to drain the coolant again and R&R the intake manifold
and gasket.  I haven't checked the main seals for leaks yet.

This ruined the more expensive ($55) coated Rover intake gasket.
I should have at least one of the cheaper uncoated Buick gaskets
on hand.  Pulling the intake isn't that big of a deal.  It's
just tedious scraping all the old RTV off and making sure
nothing drops into the engine.  At least I can take advantage
of the opportunity to verify the 2x4 barrel GM intake won't
clear the hood.

With the Erson cam and Edelbrock intake, it was running great
and I kept thinking how well it pulls with only 8:1 compression.
That got me thinking about how much better it might pull with
more compression.  With the intake off, all I need to do is
remove the alternator and bracket and headers to pull the heads.
The late 4.0L/4.6L heads have a smaller combustion chamber
which would provide a quick boost in compression.  I wrote
a routine to calculate compression and used the specs for
the Silvolite 1718 pistons.  Running the nominal values for
a TR8, I got just under 8:1 compression which is reasonably
close to the 8.13:1 TR8 rating.  Inputs were:

 5.66" rod length
 3.6" diameter headgasket bore
 3.5" bore
 2.8" stroke
 8.96" deck height undecked
 8.903" deck height zero decked
 Silvolite 1718 piston
 1.843" compression height
 2.812" piston dish diameter
 0.15"  piston dish depth
 15.27 cc's dish volume
 28 or 36 cc's cylinder head volume
 3.6" diameter headgasket
 0.016" or 0.020" compressed headgasket thickness

for various combinations, I got the following compression ratios:

 1. 36 cc's chamber volume, 0.020" compressed headgasket thickness,
0.057" deck clearance
   Compression Ratio = 7.942

 2. 36 cc's chamber volume, 0.020" compressed headgasket thickness,
zero deck clearance
   Compression Ratio = 9.085

 3. 28 cc's chamber volume, 0.020" compressed headgasket thickness,
0.057" deck clearance
   Compression Ratio = 8.941

 4. 28 cc's chamber volume, 0.016" compressed headgasket thickness,
0.057" deck clearance
   Compression Ratio = 9.187

 5. 28 cc's chamber volume, 0.020" compressed headgasket thickness,
zero deck clearance
   Compression Ratio = 10.473

Going from 8:1 to 9.2:1 compression ratio without pulling the
engine would be worth it.  If the engine were out, I be tempted
to pull it apart and mill the block.

Or I could just put up with the leak until I put the 4.2L engine
together.  Originally, I wanted to convert to fuel injection over the
winter.  The plan was to leave the 3.5L installed and add the Rover
3.9L EFI manifolds.  Use that engine to debug the injection, then build
the cross-bolted main Rover 4.2L using the GM race heads and Willpower
single plane EFI intake.

Dan Jones

[BlownMGB-V8]

I had something similar happen on the blower motor, but in my case it was blowby which was ignited in the crankcase via a vent line to the blower inlet. My brother was driving the car at the time and it blew the valley cover wide open and launched the breather cap into oblivion. In retrospect I guess it's better than blowing up something more expensive.

Sounds like you have so many toys to play with that the problem is choosing. Not a bad spot to find yourself in.

Jim